Beasts are one of the primal races, specifically those who are awakened by an animal (sometimes refered to as a spirit animal) and later being to show more animalistic features. The first awakened of the Beasts is Grayhorn, who meets all when they awaken.
From tales that have been told, Beast's were slowly shaken awake by the behaviour of animals in their dreams. Sometimes they were attacked by the animal, others followed them out of curiousity and fracturing the pattern they had been in for such a long time. Something about that animal stuck with them, be it their spirit or body and as they awoke they were changed that way forever, whether or not they knew it at the time.
At first, beasts don't notice any physical change, nor does anyone else. After about a day, the beast
notices their spirit animal with them everywhere... then doesn't notice it anymore as it becomes normal. Changelings who can see through spirit veils can see these animals with their Changeling, such as priests and other beasts. After a while, when the Beast becomes more aware of the Dreamscape and slowly more powerful, they begin to take on the form of their spirit animal, as the two become more in tune with each other. Grayhorn appears to have discovered a way to controll his shape, though other Beasts have not, so appear more bestial than him.
Beasts tend to find niches in Changeling society that suits them and their spirit animal. More carnivorous Beasts find themselves in roles that lead to more combat, whilst many herbivorous Beasts find themselves farming or trading. The one thing that all the Beasts share is a love and understanding of nature, even if some are city folk as well.